The present invention relates to an acoustically tuneable light source and method for acoustically tuning a light source.
Tuneable light sources output light comprising at least one of a plurality of frequencies. One type of tuneable light source, the tuneable distributed feedback (DFB) laser, has found applications in optical communications. The tuning time for DFB lasers, however, is on the order of milliseconds, which is slower than the microsecond tuning times required for modern optical communication systems.
Another example of a tuneable light source is a diode-pumped, packaged acousto-optically tunable Ti:Er:LiNbO3 waveguide laser described by K. Schafer et al., IEEE J. Quant. Electr., v.33, , #10, pp.1636-1641. This laser provides sub-millisecond tuning capability through TE-TM mode conversion within birefringent material. It would be desirable, however, to form a tuneable laser from non-birefringent materials, such as non-crystalline materials, because birefringent materials are more complex in manufacturing and operation.
A first embodiment of the invention relates to a light source. The light source comprises first and second optical waveguides, at least one of which waveguides comprises a gain medium. Upon excitation, such as by irradiation with light from a light source, the gain medium generates, such as by emitting, light having a plurality of frequencies, at least some of which may be output by the light source. The particular frequencies of light output by the light source may be acoustically switched at more than about 100 kHz.
The first and second waveguide define a first optical coupling region, wherein light, such as the generated light, propagating along one of the waveguides may couple to the other waveguide. Preferably, only light that couples between waveguides may be output by the tuneable light source. The optical frequency that couples between waveguides may be acoustically switched by subjecting the first optical coupling region to acoustic waves having a longitudinal frequency xcfx89AC1. Essentially the only light that may couple is light that satisfies a matching condition of the first coupling region whereby, upon coupling, a frequency of the light is shifted by about xc2x1xcfx89AC1.
A second embodiment of the present invention is related to an integrated laser cavity that may be used to generate laser light. The laser cavity comprises first and second optical waveguides, which define an offset coupling region therebetween. By offset it is meant that longitudinal axes of the first and second optical waveguides are spaced apart from one another. At least one of the optical waveguides comprises a gain medium configured to, upon excitation, generate light.
Light propagating along one of the first and second waveguides may couple to the other waveguide at the coupling region. The frequency of light that may couple is acoustically tuneable by varying a first longitudinal acoustic wave vector KAC of acoustic waves impinging upon the first coupling region. Upon coupling from one waveguide to the other, a wave vector of the coupled light is shifted by an amount KAC. Preferably, only light that couples may be output by the integrated laser cavity.
Another embodiment of the invention relates to an integrated interferometer having at least first and second different optical paths. The interferometer includes first and second coupling regions, whereby light propagating along the first and second optical paths couples interferingly to a first waveguide and propagates therealong. A first acoustic wave source subjects the first and second coupling regions to acoustic waves having a first longitudinal acoustic wave vector KAC1, whereby a wave vector of light propagating along one of the first and second optical paths differs from a wave vector of light propagating along the first waveguide by an amount KAC1.
Another aspect of the invention relates to a method for producing light. In one embodiment, a gain medium within a first waveguide is irradiated with pump light to obtain generated light having an generated light frequency. The generated light is coupled to a second waveguide by subjecting at least some of the generated light to acoustic waves having a first frequency xcfx89ACi to thereby provide second light having a second light frequency, wherein the second light frequency differs from the emitted light frequency by an amount xcfx89ACi. At least some of the second light is output.
Another aspect of the invention relates to an optical transmitter that includes an optical cavity comprising an optical coupling region between first and second waveguides. An acoustic wave source is disposed to subject the optical coupling region to acoustic waves having an acoustic frequency xcfx89i, whereby, upon coupling from one waveguide to the other, a frequency of light oscillating within the optical cavity is shifted by an amount of about xc2x1xcfx89i. The optical cavity is configured to output at least some of the oscillating light. The transmitter also includes an acoustic wave source driver for changing the acoustic frequency xcfx89i, wherein a frequency of light output by the optical cavity changes upon changing the acoustic frequency xcfx89i.
Light transmitted by the optical transmitter may be received by a receiver that simultaneously detects the transmitted light with light output by an acousto-optically tuneable optical cavity local to the receiver.